Use better command-line options for server

From jekyll --help:
        --[no-]safe                  Safe mode (default unsafe)
        --[no-]auto                  Auto-regenerate

Safe mode is used on GitHub Pages, so it's good to use by default.

Auto mode regenerates your site automatically whenever files change. Except _config.yml, because #reasons.
Merge pull request #1 from krallja/patch-1

Use better command-line options for server